The present technology relates to a resonant switching power supply apparatus used in various electronic devices such as a television set.
Various different resonant switching power supply apparatuses have been proposed (for example, see Japanese Patent Application Laid-open No. 2005-198457, hereinafter referred to as Patent Document 1).
FIG. 1 is a circuit diagram illustrating a structure of a switching power supply apparatus (resonance circuit) disclosed in Patent Document 1.
The switching power supply apparatus illustrated in FIG. 1 has a series circuit including a first switching element (high-side switching element) 2 and a second switching element (low-side switching element) 3, and connected to both ends of a DC power 1.
A gate terminal of each of the first switching element 2 and the second switching element 3 is connected to an output terminal for a gate signal that is a drive control pulse from a control circuit 9. The first switching element 2 and the second switching element 3 are alternately turned on or off.
Furthermore, the second switching element 3 is connected in parallel to a series circuit including a resonance capacitor 7 and a primary side inductor 5 among the primary winding (coil, inductor) 5 and a secondary winding 6, between which are insulated, of a transformer 4. Furthermore, the resonance capacitor 7 is connected in series to a current detection unit 8 including a resistive element.
For a period of time during a current through the first and second switching elements 2 and 3 flows through one of body diodes of the elements 2 and 3, a control circuit 10 inhibits inversion of a gate signal, so that the on-state of a switch through which this current flows is maintained.
When an off-resonance condition is detected, the control circuit 10 inverts a gate signal to the switching elements 2 and 3 after a current through the switching elements 2 and 3 flows through the body diodes thereof.
This switching power supply apparatus (resonance circuit) employs a technology to avoid destruction of the first switching element 2 and the second switching element 3 due to excessive stress induced by a di/dt mode, etc., by reducing an oscillatory frequency of a power supply when an off-resonance condition is present.